People with flat feet usually can run fast and are less likely to become injured. During World War II, having flat feet would have kept you out of the army, but a study published in the Archives of Family Medicine (July 1993;21:64) shows that army recruits who have the flattest feet suffer the fewest injuries.
Healthy army recruits had their arches measured before they started 12 weeks of basic training. Those with the flattest feet had the fewest injuries. When you run, you land on the outside bottom of your feet and roll inward to absorb the hard shock of your foot striking the ground. Most people who have flat feet have normal arches. Their feet appear flat because they have flexible ankles that allow their feet to roll so far inward that their arches touch the ground, so you can’t see them. The more you roll in, the greater the shock absorption and protection from injury. People with flat feet also are often fast runners because rolling in allows their feet to press harder on the ground to force them forward with greater force.